High voltage battery packs can be configured for efficient space utilization by stacking and co-packaging battery cells of a prismatic (i.e., rectangular) form factor. The prismatic cells are typically arranged so that their terminals are all accessible from the top of the pack, and the terminals of adjacent cells lie in close proximity for convenient interconnection due to the thin profile of the cells. Lithium-ion batteries are well-suited to such applications because of their low weight, high power density and relatively high cell voltage, and because they can be produced at relatively low cost in prismatic form, particularly when encapsulated by a soft package of metalized plastic film instead of a rigid plastic or metal case. When soft-package cells are used, they can be conveniently mounted in stackable rigid plastic frames, as shown for example, in the U.S. Patent Publication No. 2006/01232119. Also, foam pads can be used for cell-to-cell isolation and to compressively support the cells.
A serious challenge involved in the design of a battery pack is the provision of adequate cooling for the individual cells. This is particularly true in hybrid vehicle and other applications that require the battery pack to supply large amounts of energy at a high rate. The usual approach is to attach one or more liquid-cooled or air-cooled heatsinks to the bottom and/or sides of the battery pack, and to use metal heat runners to transfer heat from the battery cells to the heatsinks by conduction. While this approach can be effective if sufficient space is available to accommodate the heatsinks, space and weight considerations often take precedence, forcing sub-optimal sizing and placement of the heatsinks. Moreover, the effectiveness of this approach is hampered for two additional reasons: first, the heat produced in a battery cell is greatest near its terminals, which may be separated from the heatsinks by a substantial distance; and second, the cooling medium rises in temperature as it travels through the heatsink, which degrades heat rejection capability at the downstream end of the heatsink. And since over-heating can permanently damage a battery cell, the power output of the battery pack often has to be limited to preserve battery pack life expectancy. Accordingly, what is needed is a way of more effectively and uniformly cooling a prismatic-cell battery pack so that its life and performance will not be heat-limited.